1. Field of the Invention
This invention relates to a construction of a water intake or guide portion of a hydraulic machine, such as a water turbine, pump, pump water-turbine, and the like, and a method for fabricating same.
2. Description of the Prior Art
A water intake portion of a hydraulic machine, in general, consists of a casing and a speed ring continuous with the casing, while the speed ring consists of a pair of members positioned between the aforesaid casing and guide vanes, and stay vanes which interconnect the aforesaid pair of members, the stay vanes being confined between the aforesaid pair of members. A pair of the members used in a conventional speed ring are provided in the form of steel plates of a large gage or thickness, each of which has an inner circumferential edge formed with a reinforcing rib serving as a coupling flange, and an outer circumferential edge which runs along the curved contour of the casing and is welded thereto.
However, difficulties are confronted with non-destructive inspection of weld joints of curved portions of a steel plate having a large gage, and thus it appears impossible to conduct the non-destructive inspection of such joints in the setting-up site of a hydraulic machine, because of no equipment available and safety problems.
It has been a general practice that such a non-destructive inspection should be conducted in a plant, in which such inspection equipments are available. On the other hand, it is customary that the aforesaid pair of members are formed into a rectangular box-like shape in cross section, due to an increase in capacity of a hydraulic machine and due to a need to reduce the manufacture cost of the hydraulic machine. With such an arrangment, a modulus of section may be increased, so that plates of a small gage may be used.
The construction of the speed ring of a box type increases difficulties in welding operation, with the accompanying expenditure of much time and effort due to complexity of the construction.
Another attempt has been proposed for a speed ring, in which a pair of members each having I shaped cross section and made of steel plates of a small gage are used to take advantages of a large modulus of section. However, in such a construction three members, including one of edges defining an opening of a casing, have to be welded at one position.
This attempt is considered to aim at reduction in amount of members forming the casing by minimizing the diameter of the casing. However, the heat affected zones of such welds are necessarily subjected to lowering in strength, due to repeated applications of heat by at least three welding operations.